Fix CKEditor height in dashboard actions form

Not wrapping the editor in a `.ckeditor` div made it change height when
the editor was loaded. That caused a weird effect for users, and also
made some tests fail sometimes since the position of the "Add new
document" link might change right when capybara is clicking it.

app/views/admin/dashboard/actions/_form.html.erb

@@ -34,7 +34,9 @@
       <%= f.text_field :short_description, label: false %>
     </div>
 
-    <%= f.cktext_area :description, ckeditor: { language: I18n.locale } %>
+    <div class="ckeditor">
+      <%= f.cktext_area :description, ckeditor: { language: I18n.locale } %>
+    </div>
   </div>
 </div>